Modularized system and method for urea production using a bio-mass feedstock

ABSTRACT

A modular system and method for producing urea from bio-mass includes means and steps for “homogenizing” a biomass feedstock stream having components with different bulk density BTU content into a stream having a consistent bulk density BTU content. The steps include cleaning the incoming bio-mass feedstock stream to remove non-organic matter, blending the cleaned bio-mass feedstock stream to obtain a homogeneous blend having a consistent bulk density BTU content, and milling the homogeneous blend bio-mass feedstock stream to a predetermined size no greater than 12 mm.

BACKGROUND OF THE INVENTION

The present invention relates generally to the conversion of bio-massand bio-mass waste streams via the process of bio-gasification and, morespecifically, to the conversion of bio-mass and bio-mass waste streamsto produce higher order chemicals such as urea.

Although the conversion of biomass and biomass waste streams via theprocess of bio-gasification (syngas) to produce usable products has beenaccomplished to varying degrees of effectiveness and efficiency in thepast, the gasification of bio-mass to produce urea is yet untapped. Themain technical barriers cited by the U.S. Department of Energy toutilizing bio-mass-based syngas to produce higher order chemicals suchas urea are: (1) feed process and handling; (2) gasification/conversion;(3) gas cleanup and catalytic conditioning; (4) syngas utilization; (5)process integration; and (6) process control, sensors, and optimization.

Prior art gasification systems using bio-mass as a feedstock stop at theformation of syngas. Because this syngas is of low quality, it cannot bedirectly used to produce higher order chemicals such as urea. Rather,the syngas is used to power generators or mixed with a natural gasstream being converted to urea (see technical barrier 3 above). Inaddition, the prior art requires large production units or large-scaleplants. Because of the high volume of production required by theseplants, the input material must be run through sequential processingunits before the syngas can be converted to ammonia. Because of the sizeof the plants, the plants tend to be located far away from all of theready and available sources of bio-mass feedstock, thereby increasingtransportation costs or—in the case of remote rural or geographicallychallenging areas—making it extremely difficult if not economicallyinfeasible to locate a plant or transport the bio-mass to the plant.This bio-mass feedstock, which tends to be stored in fields prior to itbeing transported to the plant and processed, is usually dirty, of lowstorage density, and difficult to handle (see technical barrier 1).Furthermore, the bio-mass feedstock varies considerably in itsprocessing characteristics both between and within types of bio-mass.This variation makes it difficult for plants to control, much lessoptimize, the conversion process and maintain a high level of conversionefficiency (see technical barriers 2 & 4-6 above).

BRIEF SUMMARY OF INVENTION

A modular system and method for producing urea from bio-mass includesthe steps of cleaning a bio-mass feedstock to remove substantially allnon-organic matter; blending the cleaned bio-mass feedstock to obtain asubstantially homogeneous blend; pelletizing the blended bio-massfeedstock to a substantially uniform size; gasifying the pellets in agasifier; and combining a resultant CO₂ stream from the gasifier withNH₃ to form urea. The cleaning step cleans the bio-mass feedstock sothat it preferably includes no more than 1% non-organic matter byweight. The cleaning step may also include the sub-step of sizing thebio-mass feedstock to a predetermined size of about 0.75 to 1.25 cm (¼to ½ in.) and reducing the bulk size of the bio-mass feedstock by about80%.

The bio-mass feedstock, which preferably has a moisture content of lessthan 15% by weight, may include a single bio-mass material havingdifferent processing characteristics or two or more bio-mass materialshaving a different processing characteristic such as density orcalorific burn value. The pelletizing step pelletizes the cleanedbio-mass feedstock and provides pellets having substantially the sameprocessing characteristics. Similarly, pellets produced from one type orquality of bio-mass feedstock may be combined and blended with pelletsproduced from another type or quality of bio-mass feedstock to produce ablend of the two pellet streams whose processing characteristics can beadjusted to maintain a consistency in temperature and burn quality forimproved or optimal gasification.

The gasifying step preferably includes the sub-step of pulverizing thepellets to a fine particle size of about 1 mm. This fine particle sizeprovides for a more efficient burn and a higher conversion rate of thebio-mass to gasified bio-mass (syngas). To further improve theefficiency and conversion performance of the gasifier, the gasifyingstep may also include the sub-step of injecting an organic oil into theinput bio-mass feed stream or mist. The feed rate to the gasifier may becontrolled so that the burn temperature of the gasifier, which may be ina range of 600° to 850° C., does not vary by more than ±25° C. Bycontrolling the quality of the incoming bio-mass, pulverizing thebio-mass to a fine particle size, and regulating the feed rate inresponse to critical process parameters, the gasifier is effective for aconversion efficiency of about 98% or more.

The resultant syngas stream from the gasifier is cleaned and thencompressed to a high pressure of about 6,000 to 7,000 psi. This pressureis roughly two times higher than the pressure used in prior art plants.The ammonia stream is processed in a bypass recycling loop system at 30%conversion rate at a high pressure of about 6,000 to 7,000 psi.

The system and method according to this invention allows for smallscale, cost effective conversion of bio-mass to higher order chemicalssuch as urea. For example, the equipment associated with each of thevarious process steps may be skid mounted or contained within thefootprint of a standard 48-foot flatbed trailer. The modules may beinterconnected at a single site or the cleaning module, pelletizingmodule, and gasifying module (and each module's associated processingsteps) may each occur at a different geographical location. Modularityalso allows the system to travel to the site of a bio-mass source, suchas a farming community located in a remote rural area, where the methodcan be practiced on site.

An object of this invention is to provide a urea production plant thathas a smaller footprint than conventional designs, is modular inconstruction, and can be easily transported, assembled for use, updated,modified, disassembled after use, and re-used. Another object of thisinvention is to provide a cost effective, low volume production plant.Another object of this invention is to provide a plant that canaccommodate a bio-mass feedstock that is typically found in most ruralareas—that is, of varying types, sizes, and process characteristics—andyet still achieve a high level of performance in converting thisnon-homogeneous bio-mass feedstock to a syngas useful in producing otherproducts. Yet another object of this invention is to provide a bio-massfeedstock that is easily handled and provides increased density, reducedstorage requirements, increased storage longevity, and reduced firehazard potential. A further object of this invention is to provide amuch cleaner and more uniform bio-mass feedstock to the gasificationprocess than current processes provide. It is yet another object of thisinvention to provide a bio-mass feedstock that burns more evenly andreduces the production of by-products such as tar. Another object ofthis invention is to provide a clean syngas to the urea/ammoniaconversion units. Still yet another object of this invention is toprovide a bypass recycling loop system run at very high pressures toachieve almost a 100% conversion rate. A final object of this inventionis to provide a process that simultaneously addresses all six of thetechnical barriers to the use of bio-mass to produce higher orderchemicals such as urea.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow diagram of a urea production process thatconverts agricultural bio-mass into urea. The agricultural bio-mass ispelletized to a consistent density prior to being fed into agasification unit.

FIG. 2 is a block layout of the feedstock preparation module arranged ona standard 48-foot flatbed trailer.

FIG. 3 is block layout of the pelletizing module arranged on a standard48-foot flatbed trailer. The pelletizing module may be skid mounted.

FIG. 4 is a block layout of the gasification system module arranged on astandard 48-foot flatbed trailer.

FIG. 5 is a block layout of the urea conversion module arranged on astandard 48-foot flatbed trailer.

FIG. 6 is a schematic representation of the interrelationship betweenthe carbon dioxide compression component, condenser/reactor, and waterextraction and drying components of the urea conversion module and thesyngas stream.

FIG. 7 is a schematic representation of the carbon dioxide compressioncomponent of an the urea conversion module.

FIG. 8 is a schematic representation of the pool condenser/reactorcomponent of the urea conversion module.

FIG. 9 is a schematic representation of the water extraction and dryingcomponent of the urea conversion module.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

All six technical barriers listed in the Background of the Inventionsection are addressed in the following technical description for theconversion of biomass via the process of gasification to produce urea.The process—which is designed for cost effective low volume production(e.g. feed rates of 1 to 5 tons per hour) and modularized for improvedprocess control and portability—provides a clean and consistent bio-massfeedstock to the gasifier. An on-demand organic oil injector is used tosupplement the bio-mass mist in the gasification unit to maintain aconstant, low fluctuating burn of the bio-mass. The gasification processalso has a feed control system that serves as a bio-mass feed regulator.The gasified bio-mass (syngas) is then cleaned by running the syngasthrough a set of cyclones (gas cleaning system-scrubbers) beforeintroducing the syngas to the ammonia/urea formation units.

Unlike the prior art systems, the process includes a bypass loop recyclesystem at 30% conversion rate run at very high pressures (about 6,000 to7,000 psi) which results in almost 100% conversion rates. The higherpressures allow for better separation of the chemical break-down duringthe creation of the ammonia. This conversion performance cannot beachieved with the same level of productivity by the high volume, lowpressure processes in common use in today's industry. These prior artprocesses run at pressures approximately one-half the pressure of theprocess described herein.

The gasification of biomass using this process can also be used withmodifications to generate other usable products. Addressing inconjunction all six of the technical barriers constitutes one of theunique features of the invention. Unlike the prior art processes, whichseek to optimize each and every step of the process, the processaccording to this invention incorporates the concept of systems“sub-optimization” developed by the American scholar and researcher Dr.W. Edwards Deming. The concept of sub-optimization states that a wholeprocess (system) may result in sub-optimized performance by optimizingeach individual sub-process (sub-system). True systems optimization isobtained by sub-optimizing sub-systems performance, when necessary, toachieve the optimization of the whole or complete system. The input ofmaterials to the process described herein goes through extra processing,namely, eight process steps of coarse to fine grinding and mixing withan additional pelletizing step. This extra processing constitutes asub-optimization of the preparatory process but leads to an overalloptimization of the complete process. Requiring additional in-processequipment, capital expenditure and processing time and effort infeedstock preparation optimizes the critical processes of gasificationand ammonia/urea production, thereby addressing all six technicalbarriers.

A urea production plant made according to this process preferablyincorporates a modular construction, another unique feature of theinvention. The plant is based on a five module configuration that isdesigned to minimize on-sight erection and start-up time/cost. The totalpackage design improves the overall reliability along with flexibility.Modular construction minimizes the footprint of the production unitswhile maintaining ease of operation and maintenance. Modularconstruction increases the ease with which updates and modifications canbe performed as well as allowing units to be built in a central locationand shipped anywhere around the world, or manufactured in the country ofoperation using standardized plans and specifications. Modularconstruction also allows for certain modules, such as the feedstockpreparation module, to travel to the source of the bio-mass feedstock.In addition, modularization allows for the upgrade of the productionplant by replacing specific modules when technical advances in suchmodules are developed without affecting the other modules that comprisethe whole system (plant). This also allows for reduced downtime forprocess upgrades and maintenance.

I. Process Description

The process for the production of urea via the gasification of bio-mass,hereinafter called the “urea plant,” includes 20 distinct process stepsas presented in FIG. 1. Each process step is herein described,specifying the instrumentation (apparatus), processing procedure,technical requirements, uniqueness of the design versus prior art, andrelated art and processes.

Process Step 1—Raw Material (Bio-Mass) Intake

The urea plant has a high degree of bio-mass feedstock flexibility. Oncethe feedstock weight, density and BTU/calorific values are known, theprocess parameters (computer numerically controlled) can be adjusted toobtain optimal gasification of the biomass. This addresses technicalbarriers 5 and 6 listed above. Bio-mass feedstocks that can be used inthis process include but are not limited to cotton gin waste, cornstover, rice hulls, sugar cane bagasse, paper goods (newspaper, officeusage, cardboard, etc.), wood (wood mills, municipal waste wood, etc.),coffee bean pulp, nutshells, straws, grasses, animal manure, mesquite,other crop residues, African palm (palm oil), and other bio-massmaterial. Any bio-mass dried to a moisture content of less than 15%,cleaned to remove non organic matter, and ground to a consistent size(via process steps 2 to 5 below) is a potential raw material stockeither alone or in combination with other dried bio-mass for theproduction of urea using this process. For example, the bio-mass that isfed into the process may include a mix of cotton gin waste,field-harvested cotton stalks, corn stover, and straw. The systemachieves high levels of efficiency, productivity, and economies as longas there is a highly blended consistent feedstock.

The consistency of the feedstock for the gasification process has been akey stumbling block that has limited the use of biomass in the past. Theraw material preparation (steps 2 through 12 in FIG. 1) addressesseveral key biomass feed issues for gasification—namely, technicalbarriers 1-3 above—and improves the overall process dependability,production throughput efficiency and productivity.

Process Step 2—Opening and Cleaning

To obtain the efficiencies and productivity of the gasification system,the raw material (biomass) must be furnished as a homogenous blend(particulate size, blend, and BTU value) in order to maintain highoperations standards and reduce the build-up of by-products that reduceprocess efficiencies and increase maintenance costs. This is achievedthrough a series of operations that remove non-organic material andblend, reduce, and condense the raw bio-mass feedstock. The preparationof the raw material begins with the opening and cleaning process wherethe biomass that is delivered to the urea plant is dumped into an openend screw conveyor that transports the raw material to the sifting andseparation process step.

Process Step 3—Sifting and Separation

In sifting and separation, when the material is being conveyed throughthe screw conveyor, the conveying is done over a fine mesh bottom toobtain the first level of raw material cleaning by removing smallnon-organic particulate matter (specifically sand) that builds up onmost biomass that is usually stored in fields and exposed to theelements.

Process Step 4—Vibrating Screened Conveyance

The next step in the process is conveying the bio-mass via an elevatedvibrating conveyor with a mesh bottom. This next step is also done toremove non-organic particulate matter. The vibrating conveyor is a moreactive removal system. This conveyor is also required to elevate thebiomass to be gravity fed to the next processing step, coarse grinding.The conveying of the material while assisting in the removal ofnon-organics can also be accomplished by such equipment as a screw augeror pneumatic conveyors that have some form of screening for removal ofnon-desirable materials from the raw material input.

Process Step 5—Coarse Grinding

Coarse grinding is the first step of the raw material preparation inwhich uniformity of size is achieved, preferably in a range of about0.75 to 1.25 cm (¼ to ½ in.). Most bio-mass, and in particular bio-massobtained from agricultural production, is a combination of differentbio-mass components (such things as husks, seeds, stalks, leaves, etc).The bio-mass, which arrives in varying sizes and shapes, is coarselyground in a gravity fed tub grinder. This size reduction not onlyachieves the first level of sizing the material but is a further step inthe raw material cleaning process and achieves about an 80% reduction inthe bulk size of the raw material. This reduction in bulk size increasesthe ability to transport and store the bio-mass raw material forprocessing. This is especially critical to plants located in regionsthat will produce enough bio-mass for year round production of urea (orother products) but the bio-mass being an agricultural byproduct (i.e.,a waste stream) is generated cyclically throughout the year (duringharvest). Efficient storage in a condensed manner is critical foreffective handling and transportation of the input stock and, inaddition, reduces storage cost. In a preferred embodiment, anapproximate 9,600 pounds per hour may be processed through this step inthe system. This step can also be achieved by such means as a hammermill or other forms of material grinding.

Process Step 6—First in Process Blending/Storage

The next step in the process uses a live bottom blending hopper with anoscillating spreader. This process achieves an increase in the blendingof the different types of bio-mass materials to achieve a higher levelof material uniformity. This step allows for an increase in raw materialquality by achieving homogeneity in the bio-mass mix. The varying typesof bio-mass that are brought in to the initial stages of the urea plantare not only non-uniform in size and type of material, but are alsonon-uniform in process characteristics such as humidity content, BTU(caloric) burn value, density, weight, and mass. The oscillatingspreader allows for a better mix of the bio-mass material and themechanical action of the live bottom blending hopper further achievesthe uniformity of size and mix of the bio-mass. This process can also beachieved by shakers and mixers.

Process Step 7—Second in Process Blending/Storage

In the next step the material is transported using an elevating conveyorwhich gravity feeds the bio-mass into a second live bottom blendinghopper with oscillating spreader (see step 6). The same processing donein step 6 is repeated in step 7.

Process Step 8—Blending Augers

Step 8 uses counter rotating screw blending augers to convey and furtherblend the bio-mass raw material. This step achieves a finer mix of thematerial and screening of nonorganic material that may still be present.This screening is achieved by a screen mesh located on the bottom of theblending auger. This process can also be achieved by a vibrating screenconveyor or other form of blending and conveyor combination.

Process Step 9—Pellet Mill Feed Storage

The blending auger (step 8) elevates the material to a live bottomblending hopper with oscillating feeder in process step 9. This servesas the pellet mill's feed storage and is a further filtering process fornon-organic material, assisting in raw material (bio-mass) size andconsistency control. The material is then gravity feed to the next step,the pellet mill—step 10). This process can also be achieved by shakersand mixers.

Process Step 10—Pellet Mill (Pelletizing)

The next step in the process is to pelletize the bio-mass. This may beachieved by using a standard pelletizer. The pellets produced may be ina range of 5/32 to ½ inch in size, with pellets in the range of ⅜ to ½inch preferred. In one preferred embodiment, pellet size ranged from5/32 to ¼ inch and a pelletized feedstock in the range of 35 pounds percubic foot to 45 pounds cubic foot was produced. In another preferredembodiment, pellet size ranged from ⅜ to ½ inch to produce a pelletizedfeedstock in the same density range as above. Other densities may beapplicable depending on the agricultural bio-mass being blended.

The pelletizing is done to reduce the size of the bio-mass to increasebulk density, reduce the potential fire hazard of bio-mass storage,reduce storage volume, improve material handling, and increase storagelongevity (because some bio-mass is seasonal it requires bulk build-upand storage for year-round availability). This process can also beachieved by bracketing or creating range cubes of the bio-mass rawmaterial.

Process Step 11—In Process Pellet Storage

The pelletized bio-mass is then sent to the gasification feed unit (step12) or to storage (step 11). Either way, the pellets are conveyed usinga screened conveyor which has cooling fans located beneath the conveyorto reduce the heat of the pellets (gained from the pelletizing process).This cooling of the pellets prevents the pellets from sweating andbuilding up heat and humidity absorption. This helps maintain bio-massquality, required for the gasification process. This process can also beachieved by any other means of conveyance that allows for cooling of thematerial, such as pneumatic conveyors.

Process Step 12—Gasification Feed Unit

To achieve the best possible gasification system, the gasifier must befurnished with a homogenous blend of raw materials (bio-mass) in orderto maintain high operations standards. This homogenous blend isprimarily accomplished via process steps 6 to 8. In step 12, thegasification feed unit is comprised of a sequential feed, six-chamber,live bottom blender. This achieves fine blending of the bio-mass bydistributing pellet physical properties and reduction of day to day rawmaterial variability. This fine blending can also be achieved by anyother means of multi-layer mixing.

Process Step 13—Gasifier (Gasification of Bio-Mass)

The gasification of the bio-mass has several sub-level process steps.First the pelletized bio-mass is run through a fine stage crusher andpulverizer. This step is critical in that the pulverizing of thepelletized bio-mass creates a uniform size reduction of bio-massparticles of less than about 1 mm. These uniform micro-particles offinely mixed and blended bio-mass provides the gasifier with materialthat can be fed in a fine mist that will burn more evenly due touniformity and size and increased surface area. This improved burncapacity reduces the probability of the production of by-products suchas tars, etc. This pulverizing step can also be achieved by means of ahammer mill or any other form of fine grinding. The bio-mass is then fedto the gasifier, which is preferably an up-draft TRME gasifier.

The gasification apparatus has several control facets that help maintainhigh levels of efficiency and quality control of the product. First,there is an on-demand organic oil injector, which is used to supplementthe bio-mass mist in the gasification to maintain a constant, lowfluctuating burn of the bio-mass. Computer numeric controls on thegasifier monitor the BTU values of the gasification and adjustaccordingly to maintain a uniform burn profile. The computer numericsensing is what triggers the on-demand organic oil injectors. Secondly,the gasification process also has a feed control system (also computernumerically controlled) that serves as a bio-mass feed regulator thatcontains a speed adjustment linked to the gasification sensors tomaintain the burn temperature at +/−25 degrees C. The speed controlspeeds up or slows down the bio-mass being fed into the gasifier whichserves to regulate the gasification temperature. This process can beachieved by other forms of gasification such as fluidized bed, bubblingfluidized bed, entrained fluidized bed or down-draft gasification units.The quality of the syngas produced addresses technical barrier 4 citedabove.

Process Step 14—Recycled Combustibles

Another sub-component of the gasification unit is the recycling of thetars which are produced by the gasification of the bio-mass. The tar ishandled by engineering the gas content to obtain a 2-to-1hydrogen-carbon ratio. A thermal cracking of the tars is achieved,breaking the long carbon chains allowing this process by-product (tar)to be re-introduced into the gasification chamber to produce usefulsyngas. The products of this whole process are syngas, CO₂, and ash. Theash is addressed in step 15 of this process description. The CO₂ isaddressed in step 16 of this process description.

The gas (syngas) produced by the gasification unit is cooled by runningit through a refrigeration loop and the temperature is dropped to lessthan about 175 degrees C. The gas is run through a multi-stagedcompression process to increase the gas pressure to about 6,000 to 7,000psi. This prepares the gas to be fed to the ammonia unit (step 17). Thiscooling and pressurization is a process requirement because without it,an incomplete ammonia reaction would result. This process can also beachieved by any other means of cooling and pressurization of a gas.

Process Step 15—Ash Disposal

In process step 13, the pelletized feedstock is efficiently gasified inexcess of 98% conversion efficiency, leaving only 6 to 9% fly ash basedon the weight of the feed material. The ash produced in this processcontains no heavy metals and is removed and can be sold as a usableproduct (fertilizer or for the production of Portland cement).

Process Step 16—CO₂ Processing

The CO₂ is removed (stripped) from the process (see step 13) and likethe syngas, is run through a multi-staged compression process to achievea pressure of about 6,000 to 7,000 psi. The compressed CO₂ is then fedto the urea production unit (see step 18).

Process Step 17—Ammonia Unit (Intermediate Ammonia Production)

This step is known technology and a Haber-Bosch ammonia unit may be usedto convert the syngas to ammonia. The ammonia produced in this processis an intermediate product required (contained) for the production ofurea and is directly fed to step 18. Other means of processing thesyngas to produce ammonia include the use of Fischer-Tropes or any otherammonia producing unit.

Process Step 18—Urea Formation

The production of urea is achieved using a pool-condenser reactor unitwhich receives both the ammonia produced in step 17 and the CO₂ createdin the gasification of the bio-mass (see step 16). The urea produced bythis unit contains a 46% nitrogen content (by weight). Any otherapparatus that converts urea from ammonia may be used at this step ofthe process.

Process Step 19—Film Dryer or Prilling (Drying of Liquid Urea)

The urea that is produced in step 18 is in liquid form. Though it can besold in this manner, the storage and ease of transportation is improvedby drying the urea. Creating a dried urea is achieved by film drying orprilling. This stabilizes the product. The choice of using a film dryeror priller is purely customer demand based.

Process Step 20—Finish Product Storage

The dried urea is a very stable and relatively inert product. Storagecan be handled in many ways and any form of storage that accounts forsome form of humidity control is an acceptable means of bulk storage forthe product.

II. Modular Arrangement

Referring now to FIGS. 2 to 5, the urea production process may be amodularized process, with process steps 1 to 5 comprising a feedstockpreparation module 100, steps 6 to 11 comprising a pelletizing module200, steps 12 to 15 comprising a gasification module 300, and steps 16to 19 comprising a urea conversion module 400. The various pieces ofprocess equipment associated with each module have been mapped to thecorresponding process steps of FIG. 1.

The feedstock preparation module 100, pelletizing module 200,gasification module 300, and urea conversion module 400 may be arrangedfor turn-key operation preferably on standard 48-foot flatbed trailersT, respectively. If a smaller size flatbed trailer is used, it may benecessary to divide the individual component parts of the module 100,200, 300, or 400 into two or more flatbed trailers with appropriateconnections being provided.

Each module 100, 200, 300, and 400 is preferably skid-mounted for easeof offloading to a remote site. A portable power plant P may be providedto power one or more of the modules 100, 200, 300, 400. The modules 100,200, 300, and 400 may be transported to and located and operated in thesame geographic location or may be individually located in differentgeographic locations. Although the process flow and interconnectionsbetween various components are not shown in FIGS. 2 to 5, a person ofordinary skill in the art would recognize the flow pattern and the typesof connections required for various process components.

Referring now to FIGS. 6 to 9, an alternate preferred embodiment of ureaconversion module 400 is shown which may be arranged so as to fit withinthe footprint of a standard 48-foot flatbed trailer T. Similar to FIGS.2 to 5 above, the various pieces of equipment associated with the ureaconversion module 400 have been mapped to the corresponding processsteps of FIG. 1.

While a modular system and method for urea production using a bio-massfeedstock has been described with a certain degree of particularity,many changes may be made in the details of construction and thearrangement of components and steps without departing from the spiritand scope of this disclosure. A system and method according to thisdisclosure, therefore, is limited only by the scope of the attachedclaims, including the fall range of equivalency to which each elementthereof is entitled.

What is claimed is:
 1. A method for producing urea from bio-mass, themethod comprising the steps of: cleaning a bio-mass feedstock to removesubstantially all non-organic matter; blending the cleaned bio-massfeedstock to obtain a substantially homogeneous blend; pelletizing theblended bio-mass feedstock to a substantially uniform size; gasifyingthe pellets in a gasifier; and combining a resultant CO₂ stream from thegasifier with NH₃ to form urea.
 2. A method according to claim 1 whereinthe bio-mass feedstock includes at least two bio-mass feedstocks eachhaving at least one different processing characteristic.
 3. A methodaccording to claim 1 further comprising the step of mixing pellets fromat least two bio-mass feedstocks each having at least one differentprocessing characteristic to produce a single substantially homogeneouspellet blend.
 4. A method according to claim 1 wherein the bio-massfeedstock has a moisture content of less than about 15% by weight.
 5. Amethod according to claim 1 wherein the cleaned bio-mass feedstockincludes no more than 1% non-organic matter by weight.
 6. A methodaccording to claim 1 further comprising the pelletizing step resultingin pellets having substantially the same density.
 7. A method accordingto claim 1 further comprising the pelletizing step resulting in pelletshaving substantially the same calorific burn value.
 8. A methodaccording to claim 1 further comprising the step of cleaning includingthe sub-step of sizing the bio-mass feedstock to a predetermined size.9. A method according to claim 1 further comprising the gasifying stepincluding the sub-step of pulverizing the pellets to a fine particlesize.
 10. A method according to claim 9 wherein the fine particle sizeis about 1 mm.
 11. A method according to claim 1 further comprising thegasifying step including at least one of the sub-steps of injecting anorganic oil into an input bio-mass feed stream and varying a feed rateto the gasifier to maintain a substantially constant burn temperature.12. A method according to claim 1 wherein a burn temperature of thegasifier when gasifying the pellets does not vary by more than about±25° C.
 13. A method according to claim 1 further comprising a burntemperature of the gasifier being in a range of from 600° to 850° C. 14.A method according to claim 1 wherein the gasifier is effective for aconversion efficiency of about 98%.
 15. A method according to claim 1further comprising the step of cleaning a resultant syngas stream fromthe gasifier.
 16. A method according to claim 1 further comprising thestep of compressing a resultant syngas stream from the gasifier to ahigh pressure of about 6,000 to 7,000 psi.
 17. A method according toclaim 1 further comprising the step of processing the NH₃ in a bypassrecycling loop at a 30% conversion rate at a high pressure of about6,000 to 7,000 psi.
 18. A method according to claim 1 wherein at leastone of the cleaning step, pelletizing step, and gasifying step occurs ata geographical location different from where at least one of the othersteps occurs.
 19. A method according to claim 1 wherein all equipmentassociated with at least one of the cleaning step, pelletizing step, andgasifying step is contained within a footprint of a standard flatbedtruck trailer.
 20. A method according to claim 1 wherein all equipmentassociated with at least one of the cleaning step, pelletizing step, andgasifying step is skid mounted.